Spiderwebs can be challenging to stitch, esp. if a stitcher doesn't know how to do couching. Here a simple charted version of a spiderweb. Use whatever threads you have, I like to do mine with metallic thread, usually a Kreinik #4 or #8 Braid but you can use what you have on hand.
If you use 14 count waste canvas, I would use 3 strands of DMC floss or 1 strand of #8 Perle Cotton or 1 strand of Kreinik #4 Braid.
If using a larger waste canvas such as 10 or 8.5 count, use 6 strands of DMC floss or #5 Perle cotton or Kreinik #8 Braid.
I make my spiders using a large round bead for the body and then a medium round bead for the head. I make the legs using 3 strands of DMC floss and straight stitches.